1. Field of the Invention
The present invention relates to a curable composition for forming a cured body by radical polymerization. More specifically, the invention relates to a novel curable composition which decreases the effect of oxygen at the time of curing without an oxygen shut-off layer which is formed by applying an oxygen shut-off material.
2. Description of the Related Art
A curable composition contains a polymerizable monomer and a polymerization initiator as basic components. When the curable composition forms a cured body by radical polymerization, an unpolymerized layer forms on the surfaces of the cured body that are exposed to the air if the step of polymerization is conducted in the air. This is because on the surfaces of the curable composition exposed to the air, oxygen in the air turns into peroxide radicals upon being bonded to the radical of the polymerizable monomer, and the polymerization no longer proceeds.
To provide a cured body without unpolymerized layer on the surfaces, it was so far attempted to radically polymerize the curable composition while shutting off the contact with the air by effecting the curing in the nitrogen atmosphere or in the water or by using an oxygen shut-off material (see, for example, patent documents 1 and 2).
Patent document 1: JP-A-2000-128723
Patent document 2: JP-A-2004-284969
A method of curing a (meth)acrylic polymerizable monomer by radical polymerization has been widely utilized in the dental field. This method has been applied to dental cements, dental adhesives (bonding materials), composite resins, resins for imparting luster to the surfaces of the resin tooth material, and tooth manicure. When the dentally restored material has an unpolymerized layer on the surfaces of the cured body, the surface hardness and color are deteriorated. Besides, the unpolymerized layer present on the surfaces gets entangled with the polishing bur at the time of polishing and grinding the cured body, and hinders the polishing work.
In the dental therapy, the above dental restorative is in many cases directly cured in the oral cavity. If there is employed a method of decreasing the formation of unpolymerized product by effecting the curing in the water or in the nitrogen atmosphere, the curable composition must be once taken out from the oral cavity causing, however, the shape formed in the oral cavity to be deformed. Formation of the oxygen shut-off layer involves difficulty in many cases and, besides, the oxygen shut-off material cannot be used for the materials having low viscosities, such as bonding materials.
Thus, the methods described in the patent documents 1 and 2 are not suited for the dental restoratives, and it has been desired to provide a technology for decreasing the effect of oxygen at the time of curing without providing oxygen shut-off layer.
On the other hand, when a radically polymerizable monomer to which a surfactant is added is used as an adhesive to a hard tissue such as teeth, there has been reported that the curable composition that is obtained stimulates the dental pulp less and permeates less into the dentin (see patent document 3).
Patent document: JP-A-7-316391
The patent document 3 further discloses adding water as a diluting solvent. However, the diluting solvent is used when a surfactant component is used as a primer. For example, the primer (often includes a radically polymerizable monomer) containing water and a surfactant is applied to the teeth and dried. Thereafter, a component containing the radically polymerizable monomer and a polymerization initiator is applied to effect the curing by polymerization. In the patent document 3, therefore, no water is existing at the time of curing, and the water does not affect the formation of the unpolymerized product.